(1) Field of the Invention
The present invention relates to an optical pickup used in an optical player/recorder that performs reproduction from and recording onto an optical recording medium such as an optical disc, a lens driving device that is a principal part of the optical pickup, and a production method for the lens driving device.
(2) Description of the Related Art
A lens driving device is used in an optical pickup contained in an optical player/recorder that reproduces data from and records data onto an optical recording medium, such as an optical disc including a CD (Compact Disc) and a DVD (digital versatile disc). This lens driving device performs focusing control to focus a laser beam on a recording surface of an optical recording medium, and tracking control to follow a track on the recording surface.
For instance, a CD loaded in a CD player/recorder rotates at a high speed (200 to 500 rotations per second), and therefore an object lens is moved frequently at short time intervals through the focusing/tracking control. Due to this driving of the objective lens, a variety of resonance frequencies inherent in the CD player/recorder are produced over a wide frequency range, which has a negative effect on a read from the optical recording medium.
A lens driving device is therefore required to have a mechanism for suppressing such resonance occurring to the objective lens over a wide frequency band including low to high frequencies.
An example of a conventional lens driving device that suppresses such resonance is disclosed in Japanese Laid-Open Patent Application No. 7-105551.
FIG. 1A is a diagrammatic view of this lens driving device 500 as the first conventional example. For ease of explanation, a fixed member 507 alone is shown in sectional view.
As shown in the figure, for the lens driving device 500, a movable member 502 carrying an objective lens 501 is supported in a cantilevered state by a fixed member 507 via four fine elastic supporting members 503-506, of which supporting members 504 and 506 are hidden by supporting members 503 and 505.
The fixed member 507 is filled with a damping material, which encloses a base portion of each of the elastic supporting members 503-506. A part of the enclosed base portion of each of the elastic supporting members 503-506 is slightly bent upward, which is considered to increase the damping material""s effect of suppressing vibrations occurring to the supporting members 503-506, especially small quick vibrations in a high frequency range.
Another example of a conventional lens driving device is disclosed in Japanese Laid-Open Patent Application No. 9-7203. FIG. 1B shows an external appearance of the second conventional lens driving device 600 in perspective view.
As shown in the figure, for the lens driving device 600, a movable member 602 carrying an objective lens 601 is supported in a cantilevered state by a fixed member 607 via four fine elastic supporting members 603-606. An end of the supporting member 603 is shaped into a form similar to a letter xe2x80x9cUxe2x80x9d to form a bent part 603a. Other supporting members 604-606 are also shaped into this form.
The supporting members 603-606 are not parallel to one another. When viewed from a direction xe2x80x9cAxe2x80x9d, the supporting members 603-606 are slanted relative to a direction perpendicular to a longitudinal direction of the supporting members 603-606, and connect the movable member 602 with the fixed member 607.
When a principal plane of each of the supporting members 603-606 is slanted as stated above, a displacement of each supporting member caused by vibrations in the focusing (vertical) direction and the tracking (horizontal) direction becomes large. By applying a damping material (not shown in the figure) to bent parts like the bent part 603a, resonance of the supporting members 603-606 is considered to be effectively suppressed.
The lens driving devices 500 and 600 of the first and second conventional technology, however, have the following problems.
The lens driving device 500 is capable of effectively suppressing resonance in the focusing direction and the longitudinal direction of the supporting members 503-506. This driving device 500, however, cannot effectively suppress a vibration in the tracking direction perpendicular to the above two directions.
With the lens driving device 500, end parts of the supporting members 503-506 are attached one by one to the movable member 502 and the fixed member 507, with the supporting members 503-508 being slightly and uniformly curved. Giving a uniform curve to all the supporting members 503-506, however, is very difficult. When the supporting members 503-506 having a different extent of the curving are used to connect the movable member 502 with the fixed member 507, the fixed member 507 supports the movable member 502 in a state of the movable member 502 being tilted relative to the fixed member 507. Such variations in the curving can actually exist between different lens driving devices, which is not desirable for obtaining correct optical information. To suppress such variations, the plurality of supporting members 503-506 need to be attached one by one while the extent of the curving of each supporting member is precisely adjusted. Such production process, however, extremely decreases the productivity.
The insert molding is considered to overcome this problem. The insert molding is performed in a manner that embeds end parts of each elastic supporting member in the movable member 502 and the fixed member 507. This production process may provide almost uniform extent of the curving to all the supporting members 503-506 although the problem of vibrations in the tracking direction still remains.
With the second conventional technology, on the other hand, a bent part is provided to each of the elastic supporting members 603-606, which are slanted in the stated manner and connect the movable member with the fixed member. This construction appears to be capable of suppressing vibrations in the tracking direction as well as the focusing direction. However, when the plurality of the supporting members 603-606 are attached one by one in the production process, a total number of production processes increases, and variations in properties of supporting members 603-606 may be caused by deformations in the supporting members 603-606 during the production process.
To reduce these variations, the elastic supporting members 603-606 may be integrally molded with the movable member and the fixed member by the insert molding as stated above. However, it is impossible to perform the insert molding using simple molds composed of a top mold, a bottom mold, and side molds since principal planes of the supporting members 603-606 are not parallel to one another. Accordingly, producing the lens driving unit 600 by the insert molding requires more pieces of molds, which makes production processes more complex.
The present invention is made in view of the above problems, and aims, as the first object, to provide a lens driving device that is capable of effectively suppressing resonance over high and low frequency bands, which is caused by the high-speed driving of the objective lens, and that can be produced with high productivity. As the second object, the present invention aims to provide a production method for such lens driving device. As the third object, the present invention aims to provide an optical pickup including the lens driving device.
The first object is achieved by a lens driving device, including: an objective lens; a first member that holds the objective lens; a second member; a plurality of supporting members that are elastic and that each include a first connected part and a second connected part that are connected respectively to the first member and the second member, so that the second member supports the first member in a manner that allows the first member to move in predetermined directions with respect to the second member; and a driving unit for driving the first member in the predetermined directions. The plurality of supporting members each include a first bent part and a second bent part that are present between the first connected part and the second connected part, the first bent part bending in a first direction, the second bent part bending in a second direction that is substantially perpendicular to the first direction.
For this construction, the first and second bent parts increase an amount of a displacement of vibrations occurring to the first member carrying the objective lens. By affixing the damping material to these bent parts, the effect of suppressing resonance can be further increased. In addition, since the first and second bent parts are bent in different directions that are perpendicular to each other, components of vibrations in all the directions are distributed to both bent parts so that a displacement of each supporting member increases. Affixing the damping material to these bent parts ensures high resonance suppressing effect over wide frequency band including high and low frequencies.
Here, each of the plurality of supporting members may be a narrow plate, and all principal planes of each supporting member, including a principal plane of the first and second bent parts, may be parallel to a certain direction that is perpendicular to a longitudinal direction of the plurality of supporting members. This allows the above lens driving device to be produced by applying side molds in the above certain direction to perform insert molding, thereby achieving mass-production of the lens driving devices having uniform properties.
The second object of the present invention can be achieved by a production method for producing a lens driving device that includes: a body structure including (a) a first member for holding an objective lens and (b) a second member for supporting the first member via a plurality of supporting members; and a driving unit for driving the first member in predetermined directions with respect to the second member to move the objective lens. The production method includes: a body structure producing step for producing the body structure; a lens affixing step for affixing the objective lens to the first member in the body structure; and a driving unit affixing step for affixing the driving unit to the body structure. The above body structure producing step includes: a supporting member producing substep for processing a plate to form the plurality of supporting members that each include a first bent part and a second bent part between both extremities of each supporting member, the first bent part bending in a first direction that is perpendicular to a principal plane of the plate, the second bent part bending in a second direction that is parallel to the principal plane and perpendicular to a longitudinal direction of the plurality of supporting members; and an injection molding substep for molding the first member and the second member by injection molding in a manner that predetermined parts of each supporting member are embedded in the first and second members. Here, each predetermined part is a connection part to one of the first member and the second member.
This production method does not require a process for connecting the plurality of supporting members one by one to the movable first member and the fixed second member. As a result, the lens driving devices achieving the high effect of suppressing resonance can be produced in volume, without varieties between different lens driving devices being produced.
The third object is achieved by an optical pickup, including: a semiconductor laser for emitting a laser beam; an objective lens for converging the emitted laser beam on an optical recording medium; a first member that holds the objective lens; a second member; a plurality of supporting members that are elastic and that each include a first connected part and a second connected part that are connected respectively to the first member and the second member so that the second member supports the first member in a manner that allows the first member to move in predetermined directions with respect to the second member; and a driving unit for driving the first member in the predetermined directions. The plurality of supporting members each include a first bent part and a second bent part that are present between the first connected part and the second connected part. The first bent part bends in a first direction, and the second bent part bends in a second direction that is substantially perpendicular to the first direction.
This construction achieves the optical pickup having very high reading precision which includes a lens driving device that can effectively suppress resonance and that can be produced with high productivity.